The various methods for the manufacture of porous glass are reviewed in U.S. Pat. No. 4,528,010. The methods include the Vycor (Corning), chemical vapor deposition, white carbon, colloid silica, and silica gel procedures.
One method of producing a porous glass body involves (1) forming an article of desired shape from a parent borosilicate glass; (2) thermally treating the glass article at a temperature of 500.degree.-600.degree. C. to separate the glass into a silica-rich phase and a silica-poor phase; (3) dissolving or leaching the silica-poor phase with acid to provide a porous structure composed of the silica-rich phase; and (4) washing to remove leaching residue, and then drying.
Embodiments for production of porous inorganic oxide glass monoliths by leaching of a soluble phase from a solid glass structure are described in U.S. Pat. Nos. 2,106,744; 2,286,275; 2,303,756; 2,315,328; 2,480,672; 3,459,522; 3,843,341; 4,110,093; 4,112,032; 4,236,930; and 4,588,540.
U.S. Pat. No. 4,584,280 describes a process for preparing a transparent porous ceramic film which involves applying an anhydrous solution containing an organometallic compound and a multifunctional organic compound to a substrate; and then thermally decomposing the organic compounds.
A more recent development is the "sol-gel" process for preparation of porous monolithic glasses and ceramics at moderate temperatures. The sol-gel procedure involves the formation of a three-dimensional network of metal oxide bonds at room temperature by a hydrolysis-condensation polymerization reaction of metal alkoxides, followed by low temperature dehydration. The resultant porous glass structure optionally can be sintered at elevated temperatures.
Embodiments for production of porous inorganic oxide glass monoliths by the sol-gel process are described in U.S. Pat. Nos. 3,640,093; 3,678,144; 3,681,113; 3,811,918; 3,816,163; 3,827,893; 3,941,719; 4,327,065; 4,389,233; 4,397,666; 4,426,216; 4,432,956; 4,472,510 (Re 32,107); 4,477,580; 4,528,010; 4,574,063; and references cited therein; incorporated herein by reference.
Of particular interest with respect to the present invention are publications relating to improvements in sol-gel processing methods for the production of porous glass monoliths.
J. Non-Crystalline Solids, 73, 669 (1985) by Scholze describes organically modified silicate monoliths produced by a sol-gel process; incorporated herein by reference.
Mat. Res. Soc. Symp. Proc., 73, 35 (1986) by Hench et al describes the role of chemical additives in sol-gel processing; incorporated herein by reference. An extensive review entitled "Use of Drying Control Chemical Additives (DCCAs) In Controlling Sol-Gel Processing" by Hench is published in "Science Of Ceramic Chemical Processing", chapter 4; John Wiley & Sons, New York (1986); incorporated herein by reference.
There is increasing interest in the development of novel types of porous inorganic oxide glass monoliths which have unique properties adapted for optical and other specialized applications.
Accordingly, it is an object of this invention to provide novel porous inorganic oxide glass monoliths.
It is another object of this invention to provide a novel sol-gel process embodiment for producing a microporous inorganic oxide glass monolith structure with exceptional properties for specialized optical applications.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
The subject matter of this patent application is related to that disclosed in copending patent applications commonly assigned Ser. No. 015,757, filed Apr. 10, 1987; Ser. No. 015,759, filed Apr. 17, 1987; and Ser. No. 015,758, filed Apr. 10, 1987.